Anterior ischemic optic neuropathy: Nonarteritic form in small and giant cell arteritis in normal sized optic discs

Abstract

By estimating cup/disc ratios in fellow eyes it has been assumed that nonarteritic anterior ischemic optic neuropathy (AION) occurs more often in small optic nerve heads. Correcting the photographic magnification we used absolute size units to measure 33 affected and 25 fellow optic discs with nonarteritic AION and 7 affected and 7 fellow optic nerve heads with arteritic AION. The affected and fellow discs with nonarteritic AION (2.37 + -0.29 mm2 and 2.31 + -0.31 mm2) were significantly (p less than 0.001, Mann-Whitney-test) smaller than 457 normal optic nerve heads (2.69 + -0.70 mm2). They were significantly (p less than 0.001; Mann-Whitney-test) larger than optic nerve heads with pseudopapilledema or drusen. Affected and fellow optic nerve heads with arteritic AION were not significantly different in size from normal discs but significantly (p less than 0.005) larger than the discs affected by nonarteritic neuropathy. There were no significant form differences between the pathologic and normal discs. Optic disc morphometry can be helpful in the differentiation of nonarteritic and arteritic AION: Nonarteritic AION occurs more often in small optic discs, arteritic AION is more often in normal sized optic nerve heads.

Racial and Ethnic Differences in Ocular Anatomy

“…Also, a smaller optic disc in whites may have some bearing on their higher prevalence of nonarteritic ischemic optic neuropathy and optic disc drusen. 60,61 Mansour 58 also reported very similar neuroretinal rim areas between black and white children. There were no differences between these races.…”

Current concepts in the diagnosis, pathogenesis and management of nonarteritic anterior ischaemic optic neuropathy

“…The retinal arterioles may be diffusely or focally narrowed, particularly in severe cases (Figure 3a). 11 The optic disc in affected eyes (if seen before onset of NAION) as well as in the contralateral eye is typically small in diameter 12,13 and demonstrates a small or absent physiologic cup (Figure 2b). [14][15][16] This 'crowded' morphologic appearance is believed to predispose the optic nerve head to ischaemia because of presumed structural crowding of the approximately 1 million axons at the level of the lamina cribrosa and has therefore been described as a 'disc-at-risk' (see below).…”

Lack of Correspondence between Early Optic Disc Oedema and Macular Ganglion Cell Loss in Non-arteritic Anterior Ischaemic Optic Neuropathy

“…It has been proposed that in NAION retinal ganglion cell losses result from obstruction of axoplasmic flow and axonal swelling due to minimal microvascular ischaemia. 1 Therefore, there is consistent correlation between the sector of the optic disc showing the earliest oedema and the visual field defect. In other words, the area of macular ganglion cell loss should correspond to the area of early optic disc oedema.…”